Tips for High Speed PCB Design
High speed pcb requires special attention to components’ location and layout, signal integrity, and EMI management. The following tips will help you realize a successful high-speed PCB design.
Impedance is the resistance or opposition of an electric circuit or component to alternating current. The wrong single-ended or differential impedance can decrease signal quality, reduce working frequency, and generate electromagnetic interference.
Controlled Impedance Routing
At high frequencies, PCB signal traces behave like transmission lines. Unless impedance matching is done, the signals may experience reflections that can distort their original data. Controlled impedance routing is a way to ensure that the impedance of a circuit board’s traces matches its components’ characteristic impedance to avoid this problem.
The impedance of a PCB trace is dependent on the width, thickness, and dielectric constant of its material. In addition, it’s also influenced by its layout and routing. For this reason, it’s important to keep a consistent geometry for your traces as much as possible. At Amitron, we use both impedance modeling software and impedance testing hardware to meet our clients’ controlled impedance requirements.
When you’re designing a PCB with controlled impedance, it’s important to know how to properly place your traces and components. This will ensure that your PCB satisfies its intended function without experiencing any interference or noise.
For example, you’ll need to route differential pair signals symmetrically and make sure that the spacing between the traces is at least 2W (or better yet, 3W). This will ensure that the traces can transfer their power without any disruptions or interference. You’ll also need to make sure high speed pcb that you use a wide enough trace width to achieve the desired impedance on your layer. It’s best to keep this value consistent across all layers.
Trace Lengths
The length of a trace can be a critical factor when it comes to high speed PCB design. The longer a trace is, the more it will lose energy due to dielectric absorption. This loss of energy results in attenuation that can be minimized by utilizing shorter traces for higher speed signals.
Signals with short traces can also suffer from crosstalk, which is the interference created between signals at different points of a circuit. This type of interference can cause noise or even short-circuiting in the system. To avoid this, make sure you have sufficient space between signal traces. You can use a PCB layout tool to simulate and optimize the location of these traces before you begin your design.
Another important consideration when it comes to trace lengths is the return path. High speed signals require a large amount of current to travel through the board. This current must then be rerouted to the correct location, which is usually the power supply. If this return path is not designed properly, it may lead to a high current density that can cause overheating.
Another essential consideration when it comes to high speed traces is their impedance matching. You can achieve this by adjusting the geometry of the traces so that their characteristic impedance takes on a specific value. This can be accomplished by using various formulas or by using a field solver utility that is integrated into your CAD software.
Decoupling Capacitors
Decoupling capacitors are a necessary part of any PCB design. Their purpose is to suppress noise generated by the power supply circuit when there is a change in load. They also help to maintain the working DC power supply voltage by storing energy when the operating current of the system is changing. They can be categorized as overall, local, and inter-board decoupling capacitors.
Local decoupling capacitors are important for high-speed signal transmission and must be located near to the active device pins they are connected to. This is due to their connection inductance with planes, which is far more critical than their nominal capacitance value. The best way to minimize this inductance is to avoid using traces on the capacitor mounting pads and to mount them as close as possible to the power or ground planes.
Another way to reduce the connection inductance of local decoupling capacitors is by placing them as close to the IC pins as possible. This will limit the time that the capacitor needs to propagate signals to the IC. For BGAs, it is a good practice to skip every other row and share each via with two power or ground balls. This will decrease the inductance of each individual ball and improve the performance of the BGA.
Power Distribution
One of the most overlooked aspects of high speed PCB design is the proper power distribution. A correctly sized power and ground plane in the board’s layer stackup can minimize signal integrity problems like return paths and electromagnetic interference (EMI) generated by switching-mode power supplies.
The correct power distribution also requires careful consideration of the impedance characteristics of High-Speed PCB Supplier the power and ground lines in the circuit. High-speed signals require very low impedances, and a power distribution system with the right impedance can help achieve these values. Using the right power supply components, such as a SMPS with a high-frequency switch, can also prevent noise spikes in the circuit’s power line that can cause problems in high-speed digital traces and devices.
Another key element of high speed pcb layout is ensuring that signal traces are free from any interconnects or stubs that could introduce additional impedance to the signal. This is especially important for differential signal traces, as the signal’s return path must be undisturbed to maintain the highest possible signal quality.
Many advanced PCB design software packages come with powerful simulation applications that can be used to examine a new design and pinpoint SI/PI/EMI issues before production. These tools can be invaluable for high-speed PCB design and manufacturing.
